There are many different technologies which can be used to produce a touch-sensitive surface including capacitive or resistive sensing and optical techniques. Capacitive multi-touch surfaces can detect the positions of one or more fingers on the surface, but cannot uniquely identify objects placed on the surface. Optical multi-touch tables, which use a camera/projector system or sensor-in-pixel technology, have the ability to identify objects equipped with a visual marker as well as sense multi-touch user input. Some technologies can only detect objects when they are actually in physical contact with the surface, whilst other technologies can detect objects which are in close proximity to the surface but are not in physical contact.